The invention relates to a rotor core for electrical machines. More particularly, the invention relates to an electric machine that includes a stator core having a stator core length and a rotor core having a rotor core length that is greater than the stator core length.
Two prior-art motors 10, 15 are shown in FIGS. 1-2, The motor 10 includes a stator core 20 and a rotor core 25 manufactured using the same number of laminations which are punched with a single tool (die). Specifically, the tool, such as a progressive die, simultaneously punches a stator lamination and a rotor lamination, which is positioned inside the stator lamination in order to reduce waste.
The motor 15 of FIG. 2 includes a stator core 20 and a rotor core 25a that have the same length. This construction is advantageous from the cost point of view, as the same number of laminations is used for both the stator core 20 and the rotor core 25a. The output of the motor 10 of FIG. 1, which uses the same stator core 20 as in FIG. 2, is improved over the output of the motor 15 of FIG. 2 due to the use of a longer rotor core 25 and magnet 30, the flux of which is axially concentrated through the stator. As a result, air-gap flux density, the stator flux linkage, the machine specific output, and/or efficiency are increased. The major drawback of this solution is the increase in cost associated with the need to produce more rotor laminations than stator laminations. The increased number of rotor laminations, as compared to stator laminations of FIG. 2, requires the manufacturer to purchase additional laminated steel and invest in supplementary tooling, which can produce rotor laminations alone, rather than the more common stator and rotor lamination combination.
The invention overcomes this disadvantage through special constructions for which an increased motor output is achieved by using approximately the same number of laminations in the stator core and rotor core.